The last time this small TNO was in its today’s position, Germans and Vikings were fighting in Europe

The discovery of a new Kuiper Belt Object is always an occasion to reflect on the lenght of its orbit and the times between two of its returns in the same orbital position. It’s the case of 2014 UZ224, a small (but not that small) Trans Neptunian Object recently discovered at about 90 astronomical units of distance from the Sun (90 times the distance Earth-Sun which is roughly 150 million km). It takes 1136 years and about 5 months for 2014 UZ224 to complete one orbit around the Sun, and the last time it was in the same position in which it was discovered, it was 880AD and the Germans were fighting Vikings in central Europe.

Orbit of 2014 UZ224

The object, which is about half as big as Pluto and twice as distant, was described yesterday in the International Astronomical Union’s Minor Planet Electronic Circulator. 2014 UZ224 is only about 530 kilometers across as average, but its size can vary a lot, depending on the albedo measurements, from 420 km(assuming an albedo of 0.4) to 1180 km (assuming an albedo of 0.05). Not that small, indeed, but quite far away from the expected size of the so called ‘Planet Nine’, whose existence was largely speculated about earlier this year. It joins a growing list of Trans Neptunian Objects known to populate the outskirts of the Solar System, but the interesting thing about its discovery is exacly how it was found.

David Gerdes of the University of Michigan led the team that found the new dwarf planet with a special camera called the Dark Energy Camera that the U.S. Department of Energy commissioned to make a map of distant galaxies.

Model rendering of the Dark Energy Camera (DECam), showing all the major components

The Dark Energy Camera operates at Cerro Tololo Inter-American Observatory, located east of the city of La Serena on the Pacific Coast in north central Chile. Despite the camera, as its name suggests, has been created to conduct a Dark Energy search survey, it’s used for other purposes as well, so we cannot talk about a serendipitous discovery. The methodology used to find new KBOs is pretty the same that was used to discover the already known objects: by comparing images of the same area taken over several days or weeks, nearby objects can be spotted as moving points against the still background of distant galaxies. This was how the team found 2014 UZ224, a single moving dot against a backdrop of the great expanse. A ‘connect the dot’ exercise, in other words, done night after night.

Currently 2014 UZ224 is the third furthest known observable Solar System object from the Sun, after Eris (96.2 AU) and V774104 (~103 AU). At its aphelion, 2014 UZ224 reaches a distance of 180 AU, which means 27 billion kilometers from the Sun.

If the International Astronomical Union (IAU) decides to add 2014 UZ224 to its official list, it would be the smallest object to be designated a dwarf planet.